A. Field of the Invention
The present invention relates to dredges and barges, and more particularly to a portable dredge which incorporates a vertically extendable and retractable leg to which an agitation propeller is mounted for producing an eroding current which will cavitate the bottom surface of a body of water and thereby dig a trench or dissipate bottom material.
It is often desirable to dig trenches or remove earth material from the bottom of a harbor, bay or river and ocean channels in order to permit passage of deep draft vessels or to remove objectionable underwater foliage. For example, sand waves in river and ocean channels must be periodically dissipated to enable vessels to pass therethrough. It has been found that agitation dredging, i.e., the use of a driven propeller for producing an eroding current of water, is a preferable method. However, in order to trench a deep furrow in a harbor or ocean floor or to enlarge and clean out a river channel or area to be enclosed by a bay, an agitation propeller must be capable of descending to considerable depths (upwards of 40 feet) and further be adjustable to permit arrangement over a variable bottom surface.
Typically, dredging machines are used to trench channels, etc. and take the form of a rather large substantial structures utilizing a shovel or scoop similar to a scoop used on a land steam shovel. The mechanical shovel or scoop is used to bring up mud, sand, rocks, etc. from a bottom surface. However, these large dredges are extremely heavy and difficult to move around and the length of the shovel boom necessarily dictates the depth to which such a dredge can dig into the bottom surface. The present invention avoids the above problem by employing adjustable agitation dredging, i.e., dredging by a propeller-driven unit secured to a vertically extendable and retractable leg which is disposed adjacent to a bottom surface and actuated to produce an eroding current for digging away or displacing sand or gravel or bottom muck for redistribution. It is desirable to have a readily portable dredge in order to increase the efficiency of digging a trench and for readily accessible movement to subsequent projects. Agitation dredging has been found to be quite efficient, and the present invention contemplates the use of an agitation prop arranged on a vertically extendable and retractable leg means which is pivotally mounted to a side portion of a dredge. The pivotal mounting enables the vertically adjustable extendable and retractable leg means and agitation prop to be stowed in a substantially horizontal position adjacent to the vessel. Such horizontal stowing is preferable when it is desired to move the portable dredge to a subsequent project or location without being impeded by the drag of a below-surfaced agitation prop. Furthermore, the present invention utilizes a retracting spud foot for materially assisting in slowing down movement of the portable dredge when conventional anchors are used off the bow and stern to secure movable enclosing lines to driven winches. Furthermore, the present invention enables the agitation prop to be swung in a substantially horizontal plane adjacent to a bottom surface in order to produce a trench having a predetermined breadth. The agitation prop may be raised or lowered by means of a winch and line for selective positioning adjacent the bottom surface.
B. Description of the Prior Art
Agitation trenching apparatuses are known in the art, and a typical example is exemplified by U.S. Pat. No. 3,440,743 which discloses an underwater trenching apparatus using axial flow propellers under the hull of a vessel for producing current flow in a direction extending aft of the hull in order to enable trenches of differing widths to be readily produced. An adjustable deflecting means is arranged aft of the propellers in order to selectively deflect the eroding current in a plurality of positions adjacent to the bottom surface to be trenched. This patent does not disclose a stowable agitation prop which may be vertically extended or retracted to enable trenching of bottom surfaces located substantially below the upper surface of a body of water. Furthermore, this patent does not disclose an impeding spud foot or the like to slow down movement of the vessel.
Another prior art patent of relevance is U.S. Pat. No. 723,122 which discloses a hydraulic dredge provided with a steam engine adapted to operate a hydraulic pump. The dredge disclosed incorporates a suction pipe adapted to be raised and lowered with a swinging frame in order to displace or wash away earth which is first loosened by a plow arrangement. The bow of the vessel is normally pivoted by means of a spud which passes through a vertical guideway in a transverse center of the bow and acts as a pivot on which the stern of a boat is adapted to swing laterally through an arc. The arc is adjusted by means of side anchors and ropes and may also be raised. However, it is readily apparent that the vessel described in this patent does not provide for flexibility of an agitation prop on a horizontally stowable vertically extendible and retractible leg.
Norwegian Pat. No. 63,383 discloses an agitation trenching device which incorporates a propeller located on the aft portion of a boat which directs a current of eroding water downward against a surface to be dug. Disposed behind the agitation propeller is a rod which apparently is placed in the bottom earth surface in order to slow the vessel down somewhat. It is readily apparent that the arrangement disclosed in this patent does not enable the trenching or digging of a channel at substantial depths below the waterline of the vessel. The disclosure in the Norwegian patent contemplates the use of an agitation prop secured to the vessel and not movable vertically with respect thereto.
Additional trenching or underwater grading devices are disclosed in U.S. Pat. Nos. 659,122, 2,856,704 and 3,010,231. These patents are deemed relevant but not worthy of further comment.